CakePHP查找条件中断提交

Question

When using the conditions paramater of find, the user id doesn't submit along with the other fields.

public function add() {
        if ($this->request->is('post')) {
            $this->Thing->create();
            if ($this->Thing->save($this->request->data)) {
                $this->Session->setFlash(__('The Thing has been saved'));
                $this->redirect(array('action' => 'index'));
            } else {
                $this->Session->setFlash(__('The Thing could not be saved. Please, try again.'));
            }
        }

$users = $this->Thing->User->find('list', array(
            'fields' => array('User.username'),
            'conditions' => array('User.ownedby' => '3')
            ));
    $this->set(compact('users'));}

Here is my view:

<div class="things form">
<?php echo $this->Form->create('Thing'); ?>
    <fieldset>
        <legend><?php echo __('Add Thing'); ?></legend>
    <?php
        echo $this->Form->input('user_id');
    ?>

    <div id="user-info">
    </div>

    </fieldset>

    <?php echo $this->Form->end(__('Submit'
    )); ?>

</div>

However, when I omit the condition parameter, it submits just fine. Any ideas? In case you were wondering, I'm using the conditions parameter to sort the list of users that results in the select dropdown this creates.

Thanks.